The party's position significantly hardened after 2013, when David Cameron promised to claw back powers from Brussels and put the renegotiated terms of Britain's membership to voters in an in/out referendum by the end of 2017 on staying in the European Union.

Back in 2011, the Tory leader dismissed the idea put forward by backbenchers to legislate for a referendum, telling MPs It was "not the right time - at this moment of economic crisis - to launch legislation that includes an in/out referendum".He was later embarrassed as a total of 81 Conservatives MPs backed a Commons motion calling for a referendum on Britain’s relationship with the EU, so the Prime Minister has clearly got the message.

Critics, like the Liberal Democrats, say that Cameron's renegotiation efforts will be "very unlikely" to produce "any significant change". Others - like Labour's Chuka Umunna - suggest Eurosceptic Tory backbenchers will spell Mr Cameron's downfall as they'll push him too far. "That party will be completely ungovernable," he told City A.M, "because it will fall apart over Europe immediately".

However, David Cameron's allies remain hopeful. Boris Johnson wrote in the Telegraph that his party leader is bound to succeesfully claw back powers "because there are so many other EU governments who now agree – shyly, bashfully, discreetly – with so much of what we are saying".

So what do the Tories want to get back? What'd be enough for success, and will David Cameron manage it?

First, get the referendum in law...

A referendum needs a change in the law. Conserative MP James Wharton drove it through the Commons in the last Parliament as a private members' bill, but it was killed off in the Lords.

This time, the Conservatives may have to get serious to ensure the latest incarnation of the bill survives passes the House of Lords. It should get through under the Salisbury Convention, which dictates that peers should not oppose the second or third reading of any government legislation promised in an election manifesto.

If the Lords do try to talk out and delay the bill, the Tories would have to drive it through using the 1911 Parliament Act, which establishes the Commons' formal dominance over the Lords. But all this could take time, and deny Mr Cameron the option of a referendum in 2016.

The Cameron demands

The Conservatives indicate they want a a looser relationship with Brussels, and a leaner European bureaucracy. "We will press for lower EU spending, further reform of the Common Agricultural Policy and Structural Funds, and for EU money to be focused on promoting jobs and growth," the party said in its manifesto.

The Tories balk at the concept of an "ever closer union", enshrined in the Treaty of Rome, the basic EU text. There is talk of winning symbolic exemption from this for Britain.

David Cameron will also push for some sort of check on EU migration, with the party lamenting that "the scale of migration triggered by new members joining in recent years has had a real impact on local communities". More than 250,000 EU citizens came to the UK last year.

The chances of capping numbers are slim: most other EU leaders consider the right to free movement to be non-negotiable. Instead, the UK government may try to reduce the "pull factors" that draw EU workers to Britain. One option would be to deny EU migrants access to in-work benefits like tax credits which increase their take-home pay.

European leaders have insisted that any attempt by Mr Cameron to curtial migration by limiting the European rules around the freedom of movement will not work, with Peter Javorčík, Slovakia’s Europe minister, telling the Financial Times "they cannot be touched".

EU officials insist that such major changes are off the table. European commission chief, Jean-Claude Juncker ruled out "major" changes to the rules in February, telling the BBC: "Other points can be mentioned.”

However, EU leaders have hinted that they could support him on other moves like restricting benefits to EU migrants.Asked about the idea in January, German Chancellor Angela Merkel said: “We will look at this, we will talk about this, not only as two countries but also with our other partners. In each and every member state there's a necessity to address this issue."

What about the backbenchers?

David Cameron's troops aren't afraid to speak out. This parliament follows from the most rebellious in post-war history. Government MPs over the last five years voted against their party line in more than a third of Commons divisions (35 per cent). There were a total of 110 occasions during 2010-2015 when seven or more Conservative MPs voted against the party line. Of the top seven most rebellious MPs in the last parliament, all have been re-elected. Philip Hollobone, David Nuttall, Philip Davies, Peter Bone, Christopher Chope, Andrew Turner and Zac Goldsmith.

Coalition cushioned Mr Cameron from his Conservative "awkward squad", as Liberal Democrat support gave him a majority of 76. But now he has a overall majority of just 12, so each Tory "awkward squad" member - if they're feeling disgruntled - could make things rather inconvenient for their party leader.

Philip Hollobone

The offer of an EU referendum should keep backbenchers well-behaved initially, some argue. "The prospect of an EU referendum will prevent Conservative backbench critics from doing anything too destabilising, at least until that referendum is delivered," Professor Philip Cowley wrote in the Telegraph. "It is this that will stop the early years of the parliament resembling those of 1992 too much. But not doing anything too destabilising is not the same as not doing anything, and the potential for Conservative MPs to act as a serious constraint on the government remains considerable once the honeymoon caused by the election result fades."

What about Cameron's cabinet?

Speaking on the BBC’s Andrew Marr Show back in January, David Cameron warned that serving cabinet ministers would have to quit the government if they wanted to campaign to leave a Union which had been reorganised on the grounds he hopes to achieve.

His stance marked a break with that taken by Labour’s Harold Wilson, prime minister at the time of the only previous European referendum, in 1975. He suspended collective cabinet responsibility to allow ministers to campaign and vote according to their conscience. Mr Cameron is likely to come under pressure to do the same to avoid a damaging split in his top team. Several members of the current Cabinet - like Justice Secretary Michael Gove, Sajid Javid at Business and Iain Duncan Smith at the DWP - have all hinted in the past that they could consider voting to leave the EU.

So will Cameron get his deal?

Mr Cameron's re-election surely removes any doubt elsewhere in Europe that Britain will vote on membership. Therefore European leaders who want Britain to stay in (and most do) must now help Mr Cameron assemble a deal that can persuade the British people to remain in the EU.

Both EU diplomats and Conservative ministers alike are confident that Mr Cameron can indeed get some sort of deal in Europe, not least since Germany's Angela Merkel would rather Britain remained in.

Perhaps the real question is not whether Mr Cameron can win his referendum, but whether he can keep his party together afterwards.